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the cardiac output

1. Patients with evidence of hemodynamic compromise require immediate synchronous direct current (DC) cardioversion. This can be achieved externally or internally in the case of thoracotomy procedures. Restoration of sinus rhythm may only be temporary but may provide time to consider potentially reversible causes of SVT. Potential side effects of DC cardioversion are stroke, ventricular fibrillation, bradycardias and asystole.

2. Adenosine can be used as an alternative when hemodynamic stability is present. For patients with WPW and AF, all AV nodal blocking agents should be avoided (beta-blockers, calcium channel blockers, digoxin, adenosine) due to the risk of unopposed conduction down the accessory pathway. DC cardioversion should be used for unstable patients, with IV procainamide the drug of choice for slowing conduction down the accessory pathway.

3. Control of ventricular rate is the mainstay of treatment in stable SVT, using any one of the following agents:

(i) IV beta-blockers

Esmolol has ultra-rapid elimination and can be titrated from minute to minute. Limited by potentially negative inotropic effects. Avoid in left ventricular dysfunction. B1-receptor selective, so can be used in patients with chronic lung disease.

(ii) IV calcium channel blockers

Verapamil and diltiazem. Both are effective at controlling ventricular rates via AV nodal blockade within minutes, but also have negative inotropic properties, with diltiazem less so.

(iii) IV digoxin

Lacks vagotonic effects, and takes approximately 6 hours for full onset of action, so requires a supplemental agent in the short term.

4. Chemical cardioversion in patients not tolerating rate control, or not responding to DC cardioversion. Consider risks/benefits of need for cardioversion. Up to 50-60% will spontaneously revert to sinus rhythm. Drugs to consider for chemical cardioversion are IV procainamide, amiodarone, ibutilide, and sotalol. Increased electrolyte imbalance predisposes to drug-induced proarrhythmias